Interval field on DateHistograms will be deprecated

[polyfractal]

Today, Elasticsearch's date_histogram aggregation's interval field supports both "fixed" and "calendar" time simultaneously, choosing between the two depending on the interval's syntax (e.g. 1d is calendar, 2d is fixed). This is super confusing for users even if they read the documentation, and a very subtle bug for everyone else because intervals don't always work as they expect.

Elasticsearch is working on a PR to deprecate this functionality, and replace it with two explicit fields: fixed_interval and calendar_interval. This way the user knows exactly what they are getting.

The plan as it stands today:

• Add fixed_interval / calendar_interval fields to date_histogram aggregation.
• Deprecate interval field in 7.0+
• Remove interval field in 8.0
• All three fields are mutually exclusive
• Changes also affect rollup configurations and composite aggs (since they both use the date_histo)

More details can be found in the PR itself (elastic/elasticsearch#33727) but I wanted to open an issue in Kibana to track the deprecation since it'll affect anything touching a date histo.

Note: we're targeting 7.0, but there's no requirement it has to make 7.0 so it could slip to 7.x

TODOs

• Courier (AggConfigs) (Add dateHistogramInterval utility #39091)
• TSVB ([TSVB] Apply dateHistogramInterval utility #39665)
• Timelion (Use new date_histogram intervals in timelion #77160)
• APM

[elasticmachine]

Pinging @elastic/kibana-app

[polyfractal]

Note: this merged into master, backport for 7.x is in-progress. I'll update when that lands as well.

[elasticmachine]

Pinging @elastic/es-ui

[elasticmachine]

Pinging @elastic/stack-monitoring

[polyfractal]

Final note, elastic/elasticsearch#41906 just merged into 7.x and backporting is now done on the ES side.

[timroes]

Update: We currently have plans to provide a utility function that autodetects this into the new data core plugin, which all teams can use. I'll update here (and via mail) once this is available.